Homopolymers of tetrahydrofuran (THF), also known as polytetramethylene ether glycols (PTMEG), are well known for use as soft segments in polyurethanes and other elastomers. These homopolymers impart superior dynamic properties to polyurethane elastomers and fibers. Copolymers of THF and at least one cyclic ether, also known as copolyether glycols, are known for use in similar applications, particularly where the reduced crystallinity imparted by the cyclic ether may improve certain dynamic properties of a polyurethane which contains such a copolymer as a soft segment. Among the cyclic ethers used for this purpose are ethylene oxide and propylene oxide. Copolyether glycols having a high molar incorporation of alkylene oxide, for example at least about 50 mol %, are desirable for higher polarity and hydrophilicity as well as improved dynamic properties, for example low temperature flexibility due to further lower crystallinity, of a polyurethane which contains such a copolymer as a soft segment.
Copolymers of THF and cyclic ether having normal molar incorporations of alkylene oxide, such as for example, from about 28 to about 49 mol %, e.g. from about 30 to about 45 mol %, are well known in the art. Their preparation is disclosed, for example, by Pruckmayr in U.S. Pat. No. 4,139,567 and U.S. Pat. No. 4,153,786. Such copolymers can be prepared by any of the known methods of cyclic ether polymerization, described for instance in “Polytetrahydrofuran” by P. Dreyfuss (Gordon & Breach, N.Y. 1982). Such polymerization methods include catalysis by strong proton or Lewis acids, by heteropoly acids, as well as by perfluorosulfonic acids or acid resins. In some instances it may be advantageous to use a polymerization promoter, such as a carboxylic acid anhydride, as disclosed in U.S. Pat. No. 4,163,115. In these cases the primary polymer products are diesters, which need to be hydrolyzed in a subsequent step to obtain the desired polyether glycols.
Other methods for manufacture of copolyether glycols having normal molar incorporations of alkylene oxide are known in the art, such as for example as shown in U.S. Pat. Nos. 4,192,943; 4,228,272; 4,564,671; and 4,585,592; and in published patent applications WO 03/076453 and WO 03/076494. For example, U.S. Pat. No. 4,564,671 discloses a process for polymerization of THF with a 1,2-alkylene oxide in the presence of a compound containing reactive hydrogen and a fixed-bed clay catalyst in which less than 30% by weight of a mixture of THF, 1,2-alkylene oxide, and a compound containing reactive hydrogen is added to the reaction mixture, which is then recycled to the reactor. U.S. Pat. No. 4,728,722 discloses such polymerization batchwise with a 1,2-alkylene oxide in the presence of compounds containing reactive hydrogen over a bleaching earth or zeolite catalyst, the 1,2-alkylene oxide being fed to the reaction mixture in such a manner that the concentration of the 1,2-alkylene oxide in the reaction mixture is kept below 2% by weight during the polymerization. U.S. Pat. No. 5,268,345 discloses polymerization of THF with ethylene oxide when montmorillonite catalyst which has been regenerated by the process disclosed therein is used. U.S. Pat. No. 4,192,943 discloses that copolyether glycol based on THF and alkylene oxides varies with the method of production. U.S. Pat. No. 4,677,231 discloses use of diluent or solvent for purification of copolyether glycol having a normal molar incorporation of alkylene oxide manufactured in a polymerization process utilizing a normal concentration of alkylene oxide as a feedstock component.
None of the above publications teach the continuous production of copolyether glycols by polymerization of a reaction mixture comprising tetrahydrofuran and a very high concentration of at least one alkylene oxide in the presence of an acid catalyst, at least one compound containing reactive hydrogen atoms, and a specific diluent or solvent. None of the above publications teach the continuous production of copolyether glycols having a high incorporation, such as, for example at least about 50 mol %, of alkylene oxide. Adjusting the methods of the above publications to produce copolyether glycols by polymerization of a reaction mixture comprising tetrahydrofuran and a high concentration of at least one alkylene oxide in the presence of an acid catalyst and at least one compound containing reactive hydrogen atoms adds complexity, processing limitations, and/or cost to the manufacturing process. A simple economical process for copolymerization of a reaction mixture comprising tetrahydrofuran and a high concentration of at least one alkylene oxide in the presence of an acid catalyst and at least one compound containing reactive hydrogen atoms to produce copolyether glycol having a high molar incorporation of alkylene oxide is needed.